Readd MD4.

Sadly this is needed by wpa_supplicant for NTLM hashes.

Change-Id: I1c362c676a11ee01f301ff6fbd33d0669396ea23
Reviewed-on: https://boringssl-review.googlesource.com/1620
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/base.h b/include/openssl/base.h
index d79d63f..bee4030 100644
--- a/include/openssl/base.h
+++ b/include/openssl/base.h
@@ -184,6 +184,7 @@
 typedef struct evp_pkey_method_st EVP_PKEY_METHOD;
 typedef struct evp_pkey_st EVP_PKEY;
 typedef struct hmac_ctx_st HMAC_CTX;
+typedef struct md4_state_st MD4_CTX;
 typedef struct md5_state_st MD5_CTX;
 typedef struct pkcs8_priv_key_info_st PKCS8_PRIV_KEY_INFO;
 typedef struct rand_meth_st RAND_METHOD;